1. Field of the Invention
This invention relates to the fabrication of non-woven, polymeric fabrics, and more particularly, this invention relates to the production of a polymeric fibrous sheet by a single step in-situ fiberization technique.
2. Description of the Background Art
Fabrics can be produced from polymers by weaving, knitting or non-woven techniques. All fabric-forming techniques require polymerization, polymer recovery and formation of filaments. In woven and knitted fabrics, the polymer is processed into filament and then into a multi-filament yarn before being woven or knitted into a fabric by interlacement of warp and weft threads. Non-woven fabrics are manufactured from a web, sheet or batt of chopped fibers that are joined by mechanical, chemical or solvent processes. Barbed needles have been used to punch into a web of fibers to entangle them. The fibers can be bonded into a felt by applying heat, moisture and pressure to a sheet of fibers. The term non-woven is also applied to fabrics comprising a web of fibers held together by sticking. The non-woven fabrics are very soft but have very little overall strength. All of these fabric forming techniques are capital and labor intensive, requiring complex multistage processing to convert raw polymer stock into knitted or woven fabric or a non-woven fibrous sheet.
A one-step process for forming shaped, fibrous polymer networks is disclosed in U.S. Pat. Nos. 4,127,624; 4,198,461; 4,397,907; and 4,403,069 by an in-situ fiberization (ISF) technique by agitation-induced crystallization of the fibers from solution. The fibers form a coherent, three-dimensional, isotropic network of crystalline fiber bundles. The three-dimensional mass of fibers is produced by cooling a container of the solution being agitated at sonic frequency. This ISF technique can be used to form a fiber mass which may subsequently be impregnated with a curable polymeric resin to provide a fiber-reinforced composite useful as a structural material or as a high strength encapsulant for electronic components. In addition, the fiber mass so formed may be broken into individual fibers or fiber bundles which are useful for forming papers, cloths, felts, mats, non-woven fabrics, cordage, and the like.
However, using these known ISF techniques, it has been found difficult to provide the fiber product in sheet form. Since the fiber product conforms to the shape of the container in which it is formed, production of self-supporting thin sheets by agitating the bulk of the solution would require closely-spaced walls to provide a narrow sheet-forming channel. Under such conditions, the generation of a fiber-forming flow field would be inhibited because of large capillary forces acting on the solution. Any material that would form under such conditions would be difficult to recover from the narrow, sheet-forming channel.
On the other hand, production of thin fiber sheets on a substrate submersed in a bulk solution would require a porous substrate surface to generate the required flow field and to prevent shake-off or dispersion of the product. In this case, the fiberized material would form as a mass entangled with the substrate and would resist separation by peeling.